Inflatable safety restraint devices have become standard equipment on many new automobiles. Many designs have developed over the years, incorporating a wide variety of components. In a typical design, an inflatable airbag or cushion is mounted in a folded state, and inflated to protect a vehicle occupant in response to an activation signal from an onboard electrical activation system. The gas generator or inflator commonly associated with the system supplies an inflation gas for filling the airbag. The inflator is typically the heaviest and most complex component in such a system. A reduction in weight and manufacturing complexity are often desirable in the automotive industry, and thus it is desirable to reduce the number and complexity of inflator parts.
Various inflator designs and methods have been utilized, for example, many systems employ an ignitable gas generant or pyrotechnic that combusts to rapidly supply inflation gases that are directed into the airbag. Many effective designs are known, however, the inherently hot gases associated with pyrotechnics and particulate material resulting from combustion thereof can present unique concerns. The hot combustion gases must, for example, be cooled to prevent damage to the system materials, particularly the airbag, and also to mitigate potential harm to vehicle occupants. Combustion of the gas generant can create noxious smoke and therefore, the gas generant compositions must be tailored to produce levels in compliance with regulatory and industry standards.
Other systems utilize a stored, pressurized gas in a canister or bottle that is released by rupturing a seal, then directed into the airbag. Advantages of the stored gas systems include lower temperatures of the inflation gases, and the lack of particulates. However, developing a fast-response, reliable system for controllably releasing the pressurized gas has proven difficult. One approach has been to combine a pyrotechnically driven projectile for rupturing the seal on the pressurized gas canister. In such a system, an onboard activation system ignites gas generants to provide an actuation gas for driving the projectile into the subject seal. These systems provide an effective means for quickly and reliably releasing the stored gas, however, relatively high velocities are required of the projectile, and after the projectile has performed its intended function, deflection and bouncing of the projectile in the apparatus may, for example, irreparably damage the associated equipment.
A further challenge to designers relates to igniting the pyrotechnic charge used to drive the projectile. Where the successful deployment of the airbag depends upon accurately and reliably igniting a relatively small pyrotechnic charge to drive a projectile, it is desirable to design a system providing reliable, repeatable performance.